Field
The present disclosure relates generally to a power conversion system and, more specifically, to a circuit for detecting the removal of an alternating current (ac) line voltage from the input of a power conversion system.
Related Art
Many electronic devices, such as cell phones, laptop computers, etc., use direct current (dc) power to operate. Power converters are used to transform ac power from conventional wall outlets to dc power that can be used as a power source by most electronic devices. Generally, these power converters employ a controller that switches a power switch between an ON state and an OFF state to control the amount of power delivered to the output of the power converter.
In some examples, the controller may include a protection circuitry that detects a fault condition of the controller and/or the power converter (e.g., over voltage condition, low voltage condition, or the like), and in response to the fault condition, can cause the ac input signal of the power converter to be removed from the input of the power converter. In this case, the power converter may include a detection circuit to indicate to the controller when the ac input signal is removed. Specifically, when the ac input signal is removed, the detection circuit can provide an indicator signal to the controller to shut down the power converter.
Typically, detection circuits include resistive elements coupled to the input of the power converter. While the circuits can be effective at detecting the removal of the ac input signal, they can also consume large amounts of power as resistive elements continuously dissipate power. Specifically, the amount of power consumed by the detection circuit may be a large portion of the overall power budget of the power converter during no-load conditions.
Additionally, some power converters may be used in a single-phase three-wire power conversion system. That is, the power conversion system can include a third terminal in addition to a line terminal and a neutral terminal that are generally included in two-wire systems. This third terminal can act as a protective earth, conducting current only during certain fault conditions (e.g., when there is a short circuit current in the system). Having a detection circuit that can operate both in a two-wire and three-wire power system to detect the removal of the ac input signal may be desirable.